Chapter 4-3 The Foundations of Physical Science MOTION Chapter 4-3 The Foundations of Physical Science

Acceleration Constant speed is easy to understand HOWEVER, ALMOST NOTHING MOVES WITH CONSTANT SPEED FOR LONG Acceleration is how we describe changes in speed or velocity Acceleration is the rate at which your speed or velocity changes

What happens if you slow down or speed up? Acceleration is easy to spot on a speed vs time graph If speed changes over time, there is acceleration

Acceleration If the hill is steeper, the acceleration is greater.

Zero Acceleration There is zero acceleration at constant speed because the speed does not change.

Constant Speed and Constant Acceleration MAKE SURE YOU DO NOT CONFUSE THE DIFFERENCE!!!! Constant speed means the object remain at the same speed the entire time Constant acceleration means an object’s speed changes by the same amount each second

Speed and Acceleration Speed and acceleration are NOT the same thing You can be moving and have no acceleration Think cruise control.

Calculating Acceleration Acceleration describes how quickly speed changes Acceleration is the change in speed divided by the change in time Let’s learn a new formula!!!!!

Let’s Solve a Problem! A sailboat moves at 1 m/s. A strong wind increases its speed to 4 m/s in 3 s. Calculate acceleration.

Solution Looking for: acceleration of sailboat Given: v1 = 1 m/s; v2 = 4 m/s; time = 3 s Formula: a = v2 – v1/t Solution: a = (4 m/s – 1 m/s)/ 3 s 1 m/s2

Acceleration on Motion Graphs The word acceleration is used for any change in speed, up or down Acceleration can be positive or negative

Positive acceleration Positive acceleration adds more speed each second. Things get faster. Speed increases over time.

Negative Acceleration Negative acceleration subtracts some speed each second. Things get slower. People sometimes use the word deceleration to describe slowing down.

Acceleration on position-time graphs The position vs. time graph is a curve when there is acceleration. The car covers more distance each second, so the position vs. time graph gets steeper each second

Free Fall An object in free fall is accelerating due to the force of gravity and no other force acting on it

Acceleration due to gravity If air friction is ignored, objects in free fall on earth accelerate downward, increasing their speed by 9.8 m/s per second Acceleration due to gravity has a value of 9.8 m/s2

Acceleration and Direction If an object’s acceleration is zero, the object can only move at a constant speed in a straight line (or be stopped) A car driving around a curve is accelerating (in the “physic’s sense”) because the direction is changing Acceleration occurs whenever there is change in speed, direction, or both

Acceleration and direction A car driving around a curve at a constant speed is accelerating because its direction is changing.

Curved Motion Curved motion is caused by sideways acceleration Sideways accelerations cause velocity to change direction, which results in turning Turns create curved motion

Projectile and Parabola Projectile - an object moving through space and affected only by gravity The action of gravity is to constantly turn the velocity vector downwards Flying objects such as birds and airplanes are not projectiles because they are affected by forces generated from their own power

Projectile and Parabola A soccer ball is an example of a projectile. A projectile is an object moving under the influence of only gravity. The path of the ball makes a bowl-shaped curve called a parabola.

Curved motion Circular motion is another type of curved motion. An object in circular motion has a velocity vector that constantly changes direction.